Passive element phase shifters are employed in radio frequency (herein abbreviated RF) transmitters for shifting the phase of a transmitted signal. One application of such phase shifters is, for example, in shifting the phase of a signal provided to each antenna in an antenna array. For example, in cellular networks, where a base station receives and transmits signals to mobile devices in a geographical cell associated with that base station, antenna arrays are used for vertically tilting downward the pattern of the electromagnetic radiation of the base station antenna, to reduce interference with neighboring cells. The phase of the signal provided to each antenna is thus shifted (i.e., relative to a reference phase) according to the required angle of tilt. The antenna array may be used to direct the beam of electromagnetic wave in a desired horizontal direction as well.
U.S. Pat. No. 5,128,639 to Ueda et al, entitled “Phase Shifter Utilizing Hybrid Element” is directed to a phase shifter, which includes a hybrid element and two phase shift regulating circuits. The hybrid element includes an input terminal, an output terminal, a coupling terminal and a through terminal. Each phase shift regulating circuit includes a distributed constant line having a characteristic impedance exceeding 50 ohms and a Field Effect Transistor (FET) switch with the gate thereof connected with a resistor. Each phase shift regulating circuit is connected respectively with the coupling and through terminals of the hybrid element.
In such an arrangement, a signal applied to the input terminal is divided and directed into the coupling and through terminals of the hybrid element. After the signals outputted from these terminals are phase shifted respectively by the respective phase shift regulating circuit, they are combined with each other and taken out of the output terminal. The amount of phase shift is determined by changes of impedance in the circuit comprising the distributed constant line and the FET switch, which appear when the FET switch is turned ON and OFF. A differential phase between the ON and OFF states of the FET switch can be set at any desired level by selecting the length of the distributed constant line.
U.S. Pat. No. 7,233,217 B2 to Phillips et al., entitled “Microstrip phase shifter” is directed to a phase shifter for adjusting the electrical phase of RF signals in a high power and multi-carrier environment. The phase shifter includes a coupling arm and support architecture. The coupling arm includes a coupling ring, a wiper element, a mid-portion, a plurality of support traces, a dielectric support, an aperture, two wing portions and an arm portion. The support architecture fastens the phase shifter to a planar surface while permitting rotation of the wiper element relative to the planar surface. The planar surface includes a plurality of support traces, a first feed line and a second feed line. The second feed line includes a shaped feed line portion that corresponds with the shape of the wiper element of the coupling arm. The shaped feed line portion includes a first portion and a second portion. The location of the support traces positioned on the planar surface corresponds with the location of the support traces located on the wing portions of the coupling arm. The dielectric spacer is positioned between the coupling arm and the feed lines disposed on the planar surface. The coupling ring, the wiper element and the mid-portion have an electric length that is approximately a quarter wavelength of the propagating signal in a circuit.
The feed lines engage with the coupling ring and with the wiper element. The wiper element is capacitively coupled to the shaped feed line portion. The coupling arm is rotated via a key, interacting with a shaft, which is inserted through the aperture. As the coupling arm rotates with the wiper element they both traverse different feed lines. The phase shifter employs capacitive coupling between the moving parts. Particularly, capacitive junctions are formed between a first combination of elements that includes the wiper element, the dielectric spacer and the shaped feed line portion, and a second combination of elements that includes the conductive ring of the coupling arm, the dielectric spacer and the first feed line. The dielectric spacer prohibits a direct current path from forming between conductive elements on the coupling arm and portions of the feed lines. The capacitive junctions facilitate the transfer of an input RF signal from the phase shifter to the outputs of the first and second portions of the shaped feed line portion. The phase shifter adjusts the phase between signals in two RF feed lines by changing the electrical path lengths that RF energy travels down each respective RF feed line.
U.S. Pat. No. 7,301,422 to Zimmerman et al., entitled “Variable Differential Phase Shifter Having a Divider Wiper Arm” is directed to a phase shifter, which includes three conductive strips on PCB board 10. An input signal is supplied to the middle conductive strip and fed to a coupling point. A wiper arm is pivotally connected to the coupling point. The wiper arm includes a Wilkinson divider having quarter wavelength arms with conductive strips extending laterally from these arms. The wiper arm is rotatable about a pivot coupler. The conductive strips of the Wilkinson divider are movable with respect to the other two conductive strips on the PCB board to vary an effective path length from the Wilkinson divider to the output ports of the other two conductive strips.